1. Field of the Invention
The present invention relates generally to liquid cryogen dispensing systems, and more specifically to dosing systems that circulate liquid nitrogen from a reservoir dewar through a flexible dosing arm and injector head and release a metered droplet into a beverage, food or other product containers just before its being sealed.
2. Description of the Prior Art
The walls of metal cans are now made of aluminum and so thin that beverage packagers must depend on artificially elevated internal gas pressures to stiffen and strengthen them. Carbonated beverages do this naturally, but non-carbonated beverages need to have droplets of liquid nitrogen added to them just before the package is sealed These shots of liquid nitrogen turn to gas inside the sealed can and the walls take on added strength to resist crushing. This same requirement of internal pressure has become a requirement for companies packaging food and beverage products in thin wall plastic containers. The added pressure makes the plastic container more rigid and facilitates the process through the labeling machines as well as making the product stackable to greater heights.
A popular approach to designing liquid cryogen dispensing systems has been to position a reservoir of liquid nitrogen directly over a moving canning line and allow drops or streams of liquid nitrogen to fall down into the open can just before sealing.
One of the earliest applications of liquid nitrogen dosing systems for pressurizing containers was developed by Reynolds Metal Company (Richmond, Va) in 1982. U.S. Pat. No. 4,407,340, was issued Oct. 4, 1983, to Eric Jensen, et al., and was assigned to Reynolds. Such describes a machine that can inject predetermined amounts of cold liquefied gas into non-carbonated beverage cans just before they are sealed. Eric Jensen, et al., note that freeze-up in prior art devices due to water vapor entering the system has been a continual problem. So a float valve to maintain a constant liquid gas level in the reservoir and a gaseous shield around the exit nozzle are included in their embodiments.
Shortly thereafter in 1982, Toyo Seikan Kaisha, Ltd. (Japan), developed a similar system. U.S. Pat. No. 4,489,767, issued Dec. 25, 1984, to Morio Yamada and was assigned to Toyo Seikan. Such describes dropping liquefied gases into cans with the aid of a can-proximity sensor. The droplets of liquid nitrogen are released into the cans from a control valve and reservoir directly above. The reservoir atmosphere is allowed to pressurize, and the nitrogen vapors are directed coaxially with the liquid nitrogen droplets in a shield-gas flow to reduce nozzle freeze-up and clogging with ice from normal room humidity. Synthetic resins are also suggested as nozzle materials to help prevent nozzle freezing.
Several years later Thornton Stearns, working for Vacuum Barrier Corporation (Woburn, Mass.), described the sub-cooling of liquid nitrogen in U.S. Pat. No. 4,865,088, issued Sep. 12, 1989. When controlled amounts of liquid nitrogen are added to uncapped containers moving in an assembly line, the immediate flashing to gas when the liquid under slight hydraulic pressure is released to atmosphere pressure is prevented. This is done my making sure the liquid nitrogen is cold enough to stay a liquid at atmospheric pressure given its inherent vapor pressure.
Very recently, Vacuum Barrier Corporation (Woburn, Mass.), as assignee, was granted U.S. Pat. No. 5,743,096, issued Apr. 28, 1998, to Russell Blanton, et al. Such describes a device very similar to a commercial product of Vacuum Barrier Corporation now in widespread use for many years. Although it's hard to see in the Patent illustrations, the apparatus locates the vacuum-insulated liquid-nitrogen reservoir up and away to one side of its dosing injector head. This permits the dosing injector head to be mounted above a beverage canning assembly line. The bulky reservoir is behind the assembly line and is elevated enough to create a modest hydraulic pressure head at the control nozzle in the dosing injector head.
Unfortunately, the reservoir's rigid supply and vent conduits branch off the sides near the top. This arrangement requires clearance space that isn't always available in preexisting and ever-changing beverage packaging assembly lines. The reservoir is also unfortunately connected to the dosing injector head with a short rigid arm. This rigid arm prevents any adjustment of the hydraulic pressure head at the control nozzle and also prevents the dosing head from fitting into very tight spaces. Tilting of the dosing injector head so that the launching trajectories of the liquid nitrogen streamlets are in the same direction and optimal for high speed assembly lines must be determined before a unit is built. These variations are possible in the commercial products of Vacuum Barrier Corporation, but only as permanent modifications during manufacturing of the system. The design of the injection nozzle in these systems also makes changing metering orifices very difficult. The units must be emptied of large amounts of liquid nitrogen in order to access the metering orifice because it is part of the control valve in the dosing injector head.
Such shortcomings make prior art systems inflexible and requires many different models to be custom built to meet each new and different manufacturing environment. All of which means both the initial cost of acquisition and the cost of using the devices will be higher than is really necessary.